def nCr(n,r):
    a=b=1
    while r:
        a*=n; a%=Mod; n-=1
        b*=r; b%=Mod; r-=1
    return a*pow(b,Mod-2,Mod)%Mod

Mod=998244353
N=int(input())
S=list(input())

A,B,C,D="ABCD"
r=0
for s in S:
    if s==A or s==B:
        r+=1

print(nCr(N,r))